Following Major Thermal Injury Abstract Sepsis is a serious uncontrolled systemic inflammatory response associated with or triggered by infection and often leading to multiple organ failure and death. It has been reported to be the 10th leading cause of death in the US and the main cause of death among major burn and trauma patients and in non-coronary intensive care units. Numerical estimates of sepsis cost range from 33,865 septicemia-related deaths in the year 2002 in the United States alone (National Vital Statistics Reports, 2005) or 18 million cases worldwide at a monitory cost of $17 billion/year as an ICU sepsis patient costs six times as much to treat as a non-sepsis patient (The Surviving Sepsis Campaign, Critical Care 7(1), 2003). The central hypothesis is that gut barrier cellular and molecular mechanisms relevant to postburn intestinal leakiness and sepsis pathogenesis include converging, differential changes in gut mucosa barrier milieu with spatiotemporally-intersecting molecular circadian clock and de novo gut melatonin production dynamics on days 1, 3 and 7 following major thermal injury. This hypothesis is the most logical expansion of the principal investigator's recently published paper on postburn gut melatonin sources and targets (Int J Biol Sci, 2010). It also addresses common grounds between my melatonin work and recent circadian research that he was engaged in developing during his sabbatical at Rush University Medical Center (Fall 2009) where Drs. Keshavarzian and Turek groups (Rush and Northwestern Universities) provided strong evidence for a link between circadian molecular clock machinery and inflammation-related gut barrier pathophysiology. His melatonin data suggests endogenous pathophysiologic melatonin changes being a key determinant of gut background oxidative state thus paving the way for innovative synergistic anti-inflammatory treatments with exogenous melatonin and other drugs. Here, he seeks to examine the spatiotemporal intersection of gut melatonin and circadian clock changes converging at the level of the gut barrier in an established animal model of major burn injury. The strength of his approach is in having identified the dynamic early major postburn gut barrier microenvironment as a site where three illusive tissue injury culprits, namely, intestinal sepsis pathogenesis, peripheral gut molecular circadian clock dysregulation and extra pineal melatonin abnormalities are spatiotemporally juxtaposed and henceforth could be captured. The following specific aims are proposed for testing the central hypothesis: (1) To characterize in situ spatiotemporal changes in gut melatonin sources before and after major thermal injury, (2) To characterize in situ spatiotemporal changes in gut circadian clock molecular markers with and without major thermal injury, and (3) To determine the effect of environmental circadian disruption on gut melatonin and inflammation in the presence and absence of major thermal injury. An essential fourth final aim is: (4) To provide professional development and mentoring for the principal investigator in order to support his professional advancement and improve his ability to successfully tackle the proposed scientific aims. The author's mentoring proposal is to partner with a very active and well- funded as well as well-published research group in the area of gut inflammation and gut barrier function at Rush University Medical Center's Department of Gastroenterology. The mentoring plan is very suitable in light of the strength of the host lab and their excellent recent publications linking gut barrier abnormalities to inflammation as well as circadian clock and melatonin, albeit in IBD and alcohol models. As such, funding of this research will significantly enhance the PI's ability to remain active in his field of research and strengthen his collaboration and importantly his academic evaluation portfolio, because professional advancement at CSU is based on performance in the areas of teaching, service and research/scholarship. The publications due to this grant funding will also enhance the PI's scientific reputation and increase his ability to attract future mainstream grant funding such as SC1 and R01.